The present invention relates to a nucleic acid-immobilized substrate. More specifically, the present invention relates to a nucleic acid-immobilized substrate in which nucleic acids are securely immobilized on a carrier in the form of fine dots, useful as a DNA array and so forth.
Currently, the following two methods are mainly used for the preparation of a nucleic acid-immobilized substrate in which wherein nucleic acids are immobilized as fine dots on a carrier, for use as a DNA chip, DNA array or the like:
(1) a method utilizing immobilization of nucleic acids by physical adsorption on a base material coated with poly-L-lysine, which is used as a carrier (WO95/35505, International Patent Publication in Japanese (Kohyo) No. 10-503841/1998), and
(2) a method comprising DNA synthesis on a base material (WO97/10365).
However, a nucleic acid-immobilized substrate manufactured by the above method (1) has a drawback that, when it is used for hybridization, nucleic acids may be dropped off from the substrate, in particular, during operation processes, which leads to reduction of detection sensitivity, fluctuation of results, i.e., a problem of reproducibility and so forth. Further, as for the efficiency in immobilization of nucleic acids by the method (1), it has a drawback that short nucleic acids of about 300-mer or less such as oligomers cannot be immobilized efficiently, although longer nucleic acids can be immobilized without any particular problems.
Further, the above method (2) requires special apparatuses and reagents for synthesizing DNA on a base material and cannot be readily employed by everyone. Further, nucleic acids to be synthesized are limited to those of about 25-mer or less. Furthermore, nucleic acids longer than 10-mer cannot so easily be synthesized.
Thus, the conventional methods have problems not only of having difficulty in preparing a nucleic acid-immobilized substrate to immobilize nucleic acids of from 10-mer to 300-mer, but also of being unable to securely immobilize nucleic acids of other lengths or being unable to immobilize nucleic acids by using a simple apparatus.
The present invention has been accomplished from the above viewpoints, and an object thereof is to provide a nucleic acid-immobilized substrate in which nucleic acids are securely immobilized on a carrier in the form of fine dots irrespective of their length, and which can be prepared by using a simple apparatus.
As a result of efforts dedicated by the present inventors to achieve the above object, it was found that, if nucleic acids were immobilized through a carbodiimide group on a carrier composed of a base material carrying a compound having the carbodiimide group, nucleic acids could be securely immobilized on the carrier in the form of fine dots irrespective of their length. Also, it was found that, if nucleic acids were immobilized through an isocyanate group on a carrier composed of a base material carrying a compound having the isocyanate group, nucleic acids could be securely immobilized on the carrier in the form of fine dots irrespective of their length. Thus, the present invention has been accomplished.
The followings are provided by the present invention.
(1) A nucleic acid-immobilized substrate which comprises a carrier comprising a base material and a compound having a carbodiimide group carried by the base material, and the same kind or different kinds of nucleic acids immobilized in the form of dots through the carbodiimide group at a plurality of sites on the carrier (also referred to as xe2x80x9ccarbodiimide carrierxe2x80x9d hereafter).
(2) The nucleic acid-immobilized substrate according to (1), wherein the dots each have a substantially circular shape and a diameter of from 10 to 3000 xcexcm.
(3) The nucleic acid-immobilized substrate according to (1), wherein the nucleic acids have a chain length of from 10 to 300 nucleotides.
(4) The nucleic acid-immobilized substrate according to (1), wherein the compound having the carbodiimide group is carried on a surface of the base material through a covalent bond.
(5) The nucleic acid-immobilized substrate according to (1), wherein number of the dots in which nucleic acids are immobilized is 10 to 10,000 per cm2 of the substrate.
(6) A nucleic acid-immobilized substrate which comprises a carrier comprising a base material and a compound having an isocyanate group carried by the base material, and the same kind or different kinds of nucleic acids immobilized in the form of dots through the isocyanate group at a plurality of sites on the carrier (also referred to as xe2x80x9cisocyanate carrierxe2x80x9d hereafter).
(7) The nucleic acid-immobilized substrate according to (6), wherein the dots each have a substantially circular shape and a diameter of from 10 to 3000 xcexcm.
(8) The nucleic acid-immobilized substrate according to (6), wherein the nucleic acids have a chain length of from 10 to 300 nucleotides.
(9) The nucleic acid-immobilized substrate according to (6), wherein the compound having the isocyanate group is carried on a surface of the base material through a covalent bond.
(10) The nucleic acid-immobilized substrate according to (6), wherein number of the dots in which nucleic acids are immobilized is 10 to 10,000 per cm2 of the substrate.
According to the present invention, there is provided a nucleic acid-immobilized substrate in which DNAs are stably immobilized. Since nucleic acids can be immobilized on the substrate of the present invention without any limitation concerning the number of chains or the length of nucleic acids, various kinds of nucleic acids can simultaneously be handled on the same base material.
Furthermore, since nucleic acids are securely bound to the carrier through covalent bonds, the nucleic acid-immobilized substrate can be useful for use as a DNA chip of excellent reproducibility and quantification characteristics.
(1) Carrier
The carrier used for the nucleic acid-immobilized substrate of the present invention is provided for immobilizing nucleic acids and comprises a base material and a compound having a carbodiimide group or an isocyanate group (also referred to simply as xe2x80x9ccarbodiimide compoundxe2x80x9d or xe2x80x9cisocyanate compoundxe2x80x9d hereafter, respectively) carried by the base material.
A. Carbodiimide Carrier
(1) Base Material
The base material used for the present invention serve""s as a support for the aforementioned carrier and is not particularly limited so long as it is basically insoluble in a solvent and is in a solid or gel state at an ordinary temperature or within a temperature range around the ordinary temperature (0 to 100xc2x0 C.). The expression that the base material is insoluble in a solvent means that the base material is substantially insoluble in various solvents such as aqueous solvents and organic solvents used in various processes when the carbodiimide compounds are provided on the base material and nucleic acids are immobilized on the base material as a carrier, as will be described later, and then it is used as, for example, a DNA chip.
Materials used for such a base material of the carrier include, specifically, plastics, inorganic polymers, metals, natural polymers, ceramics and the like.
Examples of the plastics include, specifically, polyethylene, polystyrene, polycarbonate, polypropylene, polyamide, phenol resin, epoxy resin, polycarbodiimide resin, polyvinyl chloride, polyvinylidene fluoride, polyethylene fluoride, polyimide, acrylic resin and so forth. Examples of the inorganic polymers include glass, quartz, carbon, silica gel, graphite and so forth. Examples of the metals include metals that are solid at an ordinary temperature such as gold, platinum, silver, copper, iron, aluminum, magnet and paramagnet. Examples of the natural polymers include cellulose, cellulose derivatives, chitin, chitosan, alginic acid, alginic acid salts and so forth. Examples of the ceramics include apatite, alumina, silica, silicon carbide, silicon nitride, boron carbide and so forth.
The base material can be in the form of, for example, film, flat plate, fiber or the like. The size is not particularly limited.
(2) Compound having a carbodiimide group
The compound having a carbodiimide group used for the present invention include, for example, polycarbodiimides that can be prepared by the method disclosed in Japanese Patent Application Laid-open (Kokai) No. 51-61599(1976), the method of L. M. Alberino et al. (J. Appl. Polym. Sci., 21, p.190 (1990)), the method disclosed in Japanese Patent Application Laid-open (Kokai) No. 2-292316(1990) or the like, low molecular-weight carbodiimides such as monocarbodiimide and dicarbodiimide that are synthesized by a method generally used for carbodiimide production, such as dehydration of urea and desulfation of thiourea and so forth.
Specifically, the aforementioned polycarbodiimides can be prepared in the presence of a catalyst promoting carbodiimidation of isocyanate from an organic polyisocyanate compound (for example, 3-methyl-1-phenyl-2-phospholene-1-oxide).
Examples of the aforementioned organic polyisocyanate compound used for the preparation of the polycarbodiimides include, for example, 4,4xe2x80x2-dicyclohexylmethane diisocyanate, m-tetramethylxylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, crude tolylene diisocyanate, crude methylenediphenyl diisocyanate, 4,4xe2x80x2,4xe2x80x3-triphenylmethylene triisocyanate, xylene diisocyanate, hexamethylene-1,6-diisocyanate, lysine diisocyanate, hydrogenated methylenediphenyl diisocyanate, m-phenyl diisocyanate, naphthylene-1,5-diisocyanate, 4,4xe2x80x2-biphenylene diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-biphenyl diisocyanate, 3,3xe2x80x2-dimethyldiphenylmethane-4,4xe2x80x2-diisocyanate, isophorone diisocyanate and a mixture of any of these.
Polycondensation occurs upon carbodiimidation of an isocyanate group in the aforementioned polyisocyanate compounds or their mixture. In this reaction, molecular weight (polymerization degree) of the product can be controlled by adding one or more kinds of monoisocyanate in an appropriate amount at an appropriate stage to block the terminals of the carbodiimide compound. The monoisocyanate can also be added in an appropriate amount at the beginning of the polycondensation reaction. Examples of such monoisocyanate include phenyl isocyanate, (ortho, meta or para)-tolylisocyanate, dimethylphenyl isocyanate, n-butyl isocyanate, cyclohexyl isocyanate, methyl isocyanate and so forth. The polymerization degree can also be controlled by the concentration of the polyisocyanate compound or the like or the reaction time.
The terminal blocking agent may be one that can be derived from a compound having isocyanate at a terminus easily prepared by a reaction of about 1 mole of a compound having an alkyl group containing a functional group such as xe2x80x94OH, xe2x80x94NH2, xe2x80x94COOH, xe2x80x94SH or xe2x80x94NH at its terminus with 2 moles of aromatic diisocyanate.
Various kinds of substances can be mentioned as the catalyst for promoting carbodiimidation of the organic isocyanate. However, 1-phenyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 3-phospholene isomers of these compounds and so forth are preferred in view of yield and other aspects.
The polycarbodiimide is prepared without solvent or in a non-reactive organic solvent. In the present invention, one of polycarbodiimides prepared as described above or a mixture thereof can be used as the carbodiimide compound, for example. The polycarbodiimide may be partially cross-linked.
Other carbodiimide compounds that can be used for the present invention include, for example, carbodiimide compounds to which hydrophilicity is imparted by adding a polyoxyethylene chain in their molecular structures as described in Japanese Patent Application Laid-open (Kokai) Nos. 63-172718(1988) and 63-264128(1988). Low molecular weight carbodiimide compounds such as monocarbodiimide compounds and dicarbodiimide compounds can also be used for the present invention.
The carbodiimide group of the aforementioned carbodiimide compounds is highly reactive and react with most of active hydrogen groups contained in alcohols, amines, thiols, phenols, carboxylic acids and so forth. For example, reactions with a carboxylic acid, alcohol and amino group proceed as represented by the following formula (I), (II) and (III), respectively (See Frederick Kurzer, K. Douraghi-Zadeh, Chemical Reviews, 67, pp.117-135, (1967) and Andrew Williams, Ibrahim T. Ibrahim, Chemical Reviews, 81, pp.599-606, (1981)).
Rxe2x80x2CO2H+RNxe2x95x90Cxe2x95x90NRxe2x86x92Rxe2x80x2C(xe2x95x90O)OC(NHR)xe2x95x90NRxe2x80x83xe2x80x83(I)
C2H5OH+C6H5Nxe2x95x90Cxe2x95x90NC6H5xe2x86x92C6H5NHC(xe2x95x90NC6H5)OC2H5xe2x80x83xe2x80x83(II)
RNxe2x95x90Cxe2x95x90NR+Rxe2x80x2NH2xe2x86x92RNHC(xe2x95x90NRxe2x80x2)NHRxe2x80x83xe2x80x83(III)
Therefore, the carrier used for the present invention can securely immobilize nucleic acids through the carbodiimide compounds by utilizing this reactivity of the carbodiimide groups.
(3) Carrier
The carrier of the present invention used for immobilizing nucleic acids comprises the aforementioned base material and the aforementioned carbodiimide compounds carried by the base material. The term xe2x80x9cto carryxe2x80x9d used in the present specification means that the carbodiimide compounds are not substantially eliminated from the base material in various solvents such as aqueous solvents and organic solvents used when nucleic acids are immobilized on a carrier or the nucleic acid-immobilized substrate is used as a DNA chip or the like.
The aforementioned carbodiimide compounds may be carried by the carrier used for the present invention simply due to physical adhesion or chemically carried through covalent bonds or the like so long as they are carried by the base material. However, the carbodiimide compounds are preferably carried by the base material through covalent bonds on the carrier used for the present invention.
The carbodiimide compounds may be carried by a part or the whole of the base material surface as required.
As the carbodiimide compounds used for preparing a carrier in which the carbodiimide compounds are carried by the base material due to physical adhesion, a polymer compound among the carbodiimide compounds mentioned in the above (2) can be used without any particular limitation. The preferable molecular weight range thereof is from 1000 to 100,000.
Although some polycarbodiimides prepared in the presence of a catalyst promoting carbodiimidation of isocyanate from the organic polyisocyanate compound mentioned in the above (2), for example, have a molecular weight of less than 1000, the molecular weight of such polycarbodiimides can be adjusted to be within the aforementioned range by introducing polyalkylene, polyoxyalkylene, polyurethane, polyamide or the like into both termini of these polycarbodiimides through urea bonds or urethane bonds.
It is preferable for any type of carbodiimide polymer compounds carried by the carrier due to the aforementioned physical adhesion that they have 2 to 100 carbodiimide groups in a molecule. If the carbodiimide polymer compounds have less than two, that is, one carbodiimide group in each molecule, they may lack in the ability to immobilize nucleic acids. To the contrary, if they have 101 or more carbodiimide groups, viscosity may become too high, a solution thereof may not be prepared, and thus their handling property upon immobilization on the base material should be degraded, while they cause no problem concerning the performance for immobilizing nucleic acids.
Such carbodiimide polymer compounds have high adhesion to the aforementioned base material, and they are carried by the base material due to such adhesion. The carbodiimide polymer compounds are carried by the base material due to physical adhesion typically in the form of a coated film.
As a method for providing the carbodiimide polymer compounds on the base material as a coated film, known means such as spraying, dipping, brushing, stamping, vapor deposition and film coating can be employed.
The carrier carrying the carbodiimide compounds through covalent bonds will be described below.
The expression xe2x80x9ccompound having a carbodiimide groupxe2x80x9d used in the present specification for the compound having a carbodiimide group carried by the base material surface is defined as a compound independent from the covalent bond moiety present between the compound and the base material surface (that is actually a xe2x80x9cgroupxe2x80x9d, but a term xe2x80x9ccompoundxe2x80x9d is used for convenience). In the present specification, therefore, as for a carrier carrying the compound having a carbodiimide group on the base material through covalent bonds, the compounds having a carbodiimide group are explained as compounds that do not contain a functional group involved in the covalent bond with the base material surface.
The carbodiimide compounds carried through covalent bonds may be of any type of those described in the above (2). Each of the carbodiimide compounds carried by the carrier on the base material surface through a covalent bond preferably has 5 to 30, more preferably 7 to 20 carbodiimide groups in a molecule. If the number of carbodiimide groups in the carbodiimide compound is between 5 and 30, favorable ability to immobilize nucleic acids can be obtained. It is also preferable in its handling because the solution would have appropriate viscosity.
In order to obtain a carrier carrying the compound having a carbodiimide group on the base material surface through covalent bonds (also be referred to as xe2x80x9ccarbodiimide compound covalently bonded type carrierxe2x80x9d hereafter), for example, a carbodiimide compound having a carbodiimide group for immobilizing nucleic acids on the carrier and another functional group to be covalently bonded to the base material surface can be covalently bonded to a functional group of a base material having a functional group that can be covalently bonded with the functional group contained in the carbodiimide compound by an appropriate method.
More specifically, the carbodiimide compound covalently bonded type carrier can be obtained by covalently bonding a compound having two or more carbodiimide groups or having one or more carbodiimide groups and one or more functional groups other than the carbodiimide group to a functional group of a base material having, on its surface, the functional group that can be covalently bonded with one of the aforementioned carbodiimide groups or the aforementioned functional groups other than the carbodiimide group contained in the compound with leaving at least one carbodiimide group free.
As the compound having two or more carbodiimide groups or having one or more carbodiimide groups and one or more functional groups other than the carbodiimide group used to prepare the aforementioned carbodiimide compound covalently bonded type carrier, there can specifically be mentioned compounds having two or more carbodiimide groups or having one or more carbodiimide groups and one or more functional groups other than the carbodiimide group, among the carbodiimide compounds mentioned in the above (2), for example. Further, there can also be used a compound obtained by introducing a functional group to be used for the covalent bond, for example, a functional group selected from a hydroxyl group, an imino group, an amino group, a carboxyl group, an isocyanate group, an isothiocyanate group and so forth into any of the carbodiimide compounds mentioned in the above (2) by an appropriate method to prepare the carbodiimide compound covalently bonded type carrier. In addition, a compound prepared by further introducing a carbodiimide group into any of the carbodiimide compounds mentioned in the above (2) as the functional group to be used for the covalent bond can also be used for the preparation of the carrier. Known conventional methods can be employed as a method of introducing such a functional group into the carbodiimide compound.
As a base material having, on its surface, functional groups that can be covalently bonded with the carbodiimide group or a functional group other than the carbodiimide group contained in the above carbodiimide compounds used for the preparation of the carbodiimide group covalently bonded type carrier, there can be mentioned, for example, the base materials mentioned in the above (1), on which surface functional groups that can form covalent bonds are introduced. The functional group to be introduced is not particularly limited so long as it is a functional group that can be covalently bonded with carbodiimide group or a functional group that can be covalently bonded with the functional group other than the carbodiimide group contained in the aforementioned compound. Specifically, however, a hydroxyl group, an imino group, an amino group, a carboxyl group, a carbodiimide group and so forth can be mentioned. These functional groups are suitably selected depending on the functional group used for the covalent bond contained in the carbodiimide compound, and introduced into the base material surface.
The method for introducing the functional group into the base material surface is suitably selected depending on the material of the base material and the functional group to be introduced. Further, the functional group may be introduced into a part or the whole of the base material surface.
For example, in order to introduce an amino group into the whole surface of a glass base material, the glass base material can be immersed into a solution obtained by dissolving amino-substituted organoalkoxysilane such as 3-aminopropyltriethoxysilane in a suitable solvent, at about 70 to 80xc2x0 C. for about 2 to 3 hours, taken out from the solution, washed with water and dried by heating at 100 to 120xc2x0 C. for about 4 to 5 hours.
Introduction of such functional groups onto surfaces of various materials mentioned in the above explanation for the base material has been commonly carried out so far, and methods therefor have been known. Therefore, even when functional groups other than the amino group are introduced into a glass base material or the base material is made of a material other than glass, such functional groups may be introduced onto a surface of the base material by such conventional known methods.
Furthermore, some of plastic base materials among those mentioned in the above (1) have the functional groups mentioned above on the surface. These can be used as they are to prepare the carbodiimide compound covalently bonded type carrier without introducing a functional group into the base material surface. Moreover, a functional group can further be introduced into even such plastic base materials to prepare the carrier.
In order to prepare the carbodiimide compound covalently bonded type carrier used for the present invention, the compound having two or more carbodiimide groups or having one or more carbodiimide groups and one or more functional groups other than the carbodiimide group obtained as described above is reacted with the base material having a functional group that can be covalently bonded with carbodiimide groups or functional groups other than the carbodiimide group on its surface under appropriate conditions so that the functional group on the base material surface should be covalently bonded with the compound with leaving at least one carbodiimide group contained in the compound for each compound free. That is, when each of the compounds has one or more carbodiimide groups and one or more functional groups other than the carbodiimide group, the reaction can be performed under reaction conditions under which the functional group or groups other than the carbodiimide group are used for the covalent bond. When a compound having only carbodiimide groups as functional group is used, the reaction may be performed so that all of the carbodiimide groups should not be used for the covalent bond.
The carrier for immobilizing nucleic acids obtained as described above and comprising a base material and carbodiimide compounds carried by the base material can securely immobilize nucleic acids of various types and sizes by utilizing reactivity of the carbodiimide groups contained in the carbodiimide compounds.
B. Isocyanate Carrier
(1) Base Material
A base material used for the carrier for immobilizing nucleic acids according to the present invention plays a role of a support for the carrier and is insoluble in solvents. More specifically, an isocyanate group is introduced onto the surface of the base material used in the present invention as described below to serve as a carrier, and nucleic acids are immobilized thereon. The carrier with the nucleic acids being immobilized thereon is used to produce or analyze nucleic acids. The carrier is substantially insoluble in various solvents such as aqueous solvents and organic solvents used during the procedure of the above production or analysis. The base material used in the present invention is not particularly limited as long as it is insoluble in solvents as described above and basically solid or gel at the ordinary temperature or within the range of the ordinary temperature (0 to 100xc2x0 C.). Specific examples of the material for the base material of the carrier include plastics, inorganic polymers, metals, natural polymers, and ceramics.
Examples of plastics are polyethylene, polystyrene, polycarbonate, polypropylene, polyamide, phenol resin, epoxy resin, polycarbodiimide resin, poly(vinyl chloride), poly(vinylidene fluoride), poly(ethylene fluoride), polyimide, and acryl resin, etc. Examples of inorganic polymers are glass, quartz, carbon, silica gel, graphite, etc. Examples of metals are those which are solid at the ordinary temperature such as gold, platinum, silver, copper, iron, aluminum, magnet, paramagnet, etc. Examples of natural polymers are cellulose, cellulose derivatives, chitin, chitosan, alginic acid, alginate, etc. Examples of ceramics are apatite, alumina, silica, silicon carbide, silicon nitride, boron carbide, etc.
The above base materials may be in the form of, for example, film, flat plate, particle, molded product (beads, strip, wells of a multiwell plate, tube, mesh, open-cell foam, membrane, paper, needle, fiber, plate, slide, or a cell incubation container), or latex. As a matter of course, its size is not particularly limited.
(2) Production of Carrier
The carrier for immobilizing nucleic acids of the present invention is the above-described base material insoluble in solvents, having an isocyanate group on its surface. This carrier of the present invention can be obtained by, for example, a method to directly introduce an isocyanate group for immobilizing nucleic acids when used as a carrier, onto the surface of the above base material by an appropriate means, a method to allow a film-forming compound having an isocyanate group to be carried by the surface of the above base material by coating or similar means, or a method to allow a compound having an isocyanate group to be carried by the surface of the above base material through a covalent bond.
More specifically, the method of allowing a film-forming compound having an isocyanate group to be carried by the surface of the base material by coating or a similar method is carried out by, for example, dissolving a film-forming compound having an isocyanate group in an appropriate solvent if necessary, coating the resulting solution on the whole or part of the surface of the base material by means of spraying, dipping, brushing, stamp, deposition, film coating, etc., and drying the product if required. Specific examples of the compound having an isocyanate group that can be coated on the surface of the base material by the above method include polycarbodiimide compounds having an isocyanate group at its end, and trialkoxysilane having an isocyanate group such as isocyanate propyltriethoxysilane.
The compound having an isocyanate group can be allowed to be carried by the surface of the base material by, for example, covalently binding a compound having an isocyanate group and the other functional group that is capable of covalently binding to the surface of the base material, to a functional group present on the surface of the base material, which is capable of covalently binding to the above functional group of the compound, by an appropriate method. The carrier of the present invention obtained by allowing a compound having an isocyanate group to be carried by the surface of the base material insoluble in solvents through a covalent bond is excellent in durability since the compound having an isocyanate group is firmly carried by the surface of the base material through a covalent bond.
Furthermore, the method of allowing a compound having an isocyanate group to be carried by the surface of the base material through a covalent bond is exemplified by the production method as described below.
The production method is the method for producing a carrier for immobilizing nucleic acid comprising a base material insoluble in solvents and having an isocyanate group on its surface, wherein said method comprises a step of covalently binding a compound having at least two isocyanate groups, or at least one isocyanate group and at least one functional group other than the isocyanate group, or at least one isocyanate group and a halogen atom (hereinafter sometimes simply referred to as xe2x80x9cisocyanate compoundxe2x80x9d) onto a functional group on the surface of the base material insoluble in solvents, which is capable of covalently binding to the isocyanate group or to the functional group other than the isocyanate group or the halogen atom with leaving at least one isocyanate group of the compound free.
Examples of the compound having at least two isocyanate groups in its molecule used in the production method include hexamethylenediisocyanate, toluenediisocyanate, tetramethylxylenediisocyanate, naphthalenediisocyanate, etc.
Examples of the functional group other than the isocyanate group of the compound having at least one isocyanate group and at least one functional group other than the isocyanate group, or at least one isocyanate group and a halogen atom in its molecule include a hydroxyl group, an amino group, an imino group, a carboxyl group, etc. Such an isocyanate compound is exemplified by chloromethyl isocyanate, chloroethyl isocyanate, etc.
The base material insoluble in solvents used in the production method, which has, on its surface, a functional group capable of covalently binding to an isocyanate group, or a functional group other than the isocyanate group or a halogen atom of the above compound, includes those insoluble in solvents described in  less than 1 greater than B(1) on the surface of which a functional group capable of covalently binding to the above-described groups is introduced. The functional group to be introduced is not particularly limited as long as it is capable of covalently binding to an isocyanate group, or a functional group other than the isocyanate group or a halogen atom of the above compound. Specific examples thereof include a hydroxyl group, an imino group, an amino group, a carboxyl group, etc. These functional groups are appropriately selected depending on the functional group of the above isocyanate compound and bound to the surface of the base material.
The method for introducing the above-described functional groups on the surface of the base material insoluble in solvents is appropriately selected depending on the material of the base material or the functional groups to be introduced. The functional groups can be introduced on the whole or part of the surface of the base material.
For example, an amino group can be introduced onto the whole of the surface of the glass base material by dissolving amino-substituted organoalkoxysilane such as 3-aminopropyltriethoxysilane in an appropriate solvent, dipping a glass base material in the resulting solution at about 70 to 80xc2x0 C. for about 2 to 3 hours, taking the base material out of the solution to wash it with water, and heat-drying it at about 100 to 120xc2x0 C. for about 4 to 5 hours.
A functional group other than an amino group can be introduced onto the glass base material, or an amino group can be introduced onto the base material made of the material other than glass by a known method conventionally used for introducing various functional groups onto the surface of various materials as listed in the above description of the base material.
Some plastic base materials among the base materials listed in  less than 1 greater than B(1) have the above functional groups on their surface originally. In this case, such base materials can be used as they are without introducing the functional groups on their surface. It is also possible to introduce the functional groups to such plastic base materials to be used in the present invention.
In the production method, a compound having at least two isocyanate groups, or at least one isocyanate group and at least one functional group other than the isocyanate group, or at least one isocyanate group and a halogen atom is reacted with the base material insoluble in solvents, which has, on its surface, a functional group capable of covalently binding to an isocyanate group, or the above-described functional group other than the isocyanate group or a halogen atom, under appropriate conditions to covalently bind the above compound to the above functional group on the surface of the base material with leaving at least one isocyanate group of the above compound free. In other words, when the compound has at least one isocyanate group and at least one functional group other than the isocyanate group or at least one isocyanate group and a halogen atom, the reaction is carried out under such conditions that the functional group other than the isocyanate group or the halogen atom is subjected to the covalent bonding. When the compound having only an isocyanate group as a functional group is used, the reaction is carried out under such conditions that all of the isocyanate groups are not subjected to the covalent bonding.
The thus-obtained carrier for immobilizing nucleic acids according to the present invention comprising a base material insoluble in solvents and having an isocyanate group on its surface can be used to immobilize various nucleic acids utilizing the reactivity of the isocyanate group. The isocyanate group is reactive, for example, with a hydroxyl group as shown in the following formula (III) and with an amino group as shown in the following formula (IV). 
(2) Nucleic Acid-immobilized Substrate
In the nucleic acid-immobilized substrate of the present invention, the same kind or different kinds of nucleic acids are immobilized in the form of dots on a plurality of sites through the carbodiimide group or the isocyanate group on a carrier comprising the aforementioned base material and the carbodiimide compound or the isocyanate compound carried by the base material.
The expression xe2x80x9cnucleic acids are immobilized in the form of dots on a carrierxe2x80x9d in the nucleic acid-immobilized substrate of the present invention means that the site where nucleic acid are immobilized are sufficiently small so that a plurality of such sites can be provided on the carrier. The shape of the aforementioned dots is not particularly limited and suitably selected depending on the method for use, applications and so forth of the nucleic acid-immobilized substrate.
Specifically, each of the aforementioned dots on which nucleic acids are immobilized in the nucleic acid-immobilized substrate of the present invention may be in a substantially circular shape and have a diameter of from 10 to 3000 xcexcm. The preferred size of the dots is about 50 to 2000 xcexcm in diameter, more preferably about 100 to 1500 xcexcm in diameter. The substantially circular shape is not limited to a circle, but includes any shapes is near a circle such as ellipse or the like without any particular limitation. For example, the diameter of an ellipse is represented as the average value of its long diameter and short diameter.
If the diameter of the dots is less than 10 xcexcm, detection may become difficult. If the diameter exceeds 3000 xcexcm, it may become difficult to secure an appropriate number of dots per unit area. Therefore, it is preferable to use a size of the dots within the above range in order to make detection easy and secure a required number of dots per unit area.
The number of sites where nucleic acids are immobilized in the form of dots on the nucleic acid-immobilized substrate of the present invention is not particularly limited, and suitably selected depending on the method of use, applications and so forth of the nucleic acid-immobilized substrate. Specifically, however, it is preferable that the number of sites where the nucleic acids are immobilized is about 10 to 10000, more preferably about 50 to 350, per cm2 on the base material. Further, the positions of the sites where nucleic acids are immobilized in the form of dots on the nucleic acid-immobilized substrate of the present invention are also selected as required depending on the method of use, applications and so forth of the nucleic acid-immobilized substrate.
As nucleic acids immobilized on the nucleic acid-immobilized substrate of the present invention, there can be mentioned natural or synthesized DNA (including oligonucleotides) or RNA (including oligonucleotides) without particular limitation. In the present invention, nucleic acids having a chain length of 10 to 300 nucleotides, in particular, which have conventionally been difficult to be immobilized, can be immobilized. Further, nucleic acids to be immobilized may be single-stranded or double-stranded. Furthermore, in the present invention, nucleic acids having functional groups that are reactive with a carbodiimide group or an isocyanate group are usually used as the aforementioned nucleic acids. In the nucleic acid-immobilized substrate of the present invention, nucleic acids immobilized in the form of dots may be of the same kind or different kinds. If different kinds of nucleic acids are used, the positional arrangement of nucleic acids of each kind and so forth may be selected as required depending on the method of use, applications and so forth of the obtained nucleic acid-immobilized substrate.
In order to immobilize such nucleic acids on the aforementioned carrier in the form of dots, nucleic acids can be brought into contact and reacted with the carbodiimide compound or the isocyanate compound by providing a small amount of the nucleic acids in the form of dots in a required size on the sites of the carrier where the carbodiimide compound or the isocyanate compound is carried, under appropriate conditions. Through the reaction of the carbodiimide group of the carbodiimide compound or the isocyanate group of the isocyanate compound carried by the carrier with hydroxyl groups, amino groups, thiol groups, carboxyl groups and so forth contained in the nucleic acids, the nucleic acids are covalently bonded with the carbodiimide compound or the isocyanate compound. As a result, the nucleic acids are immobilized on the carrier.
Specifically, nucleic acids contained in water or a buffer are usually provided so that activity of the nucleic acids to be immobilized is maintained in their reaction of the both substances upon contact. The temperature during the reaction upon contact is preferably 0 to 100xc2x0 C. in general so that activity of the nucleic acids should not be degraded.
In the present invention, as means for providing a small amount of nucleic acids, usually provided as water or a buffer containing nucleic acids, on the carrier in the form of dots, methods using a dispenser, pin, bubble jet or the like may be employed, but the present invention is not limited to these methods. Apparatuses for providing a small amount of solution by these methods are commercially available and they can be used for the present invention.
When the nucleic acid-immobilized substrate of the present invention is used for an analysis or the like, nucleic acids other than the aforementioned immobilized nucleic acids are often brought into contact with it. In order to prevent such nucleic acids or the like other than the immobilized nucleic acids from nonspecifically binding with an unreacted carbodiimide group contained in the carbodiimide compound or an unreacted isocyanate group contained in the isocyanate compound carried by the carrier, an excess amount of bovine serum albumin (BSA), casein, nucleic acids generally used in hybridization reactions for blocking such as salmon sperm DNA or the like is preferably brought into contact with the carrier to block a free carbodiimide group or a free isocyanate group after nucleic acids are immobilized in the form of dots on the carrier as described above.
In the nucleic acid-immobilized substrate of the present invention obtained as described above, the nucleic acids are very securely carried by the carrier and are not dropped even by the washing methods widely employed for hybridization or the like (washing methods using a surfactant). Therefore, when an analysis or the like is performed by using this, the analysis is enabled with excellent reproducibility and quantification characteristics. In addition, since nucleic acids can be immobilized on the nucleic acid-immobilized substrate of the present invention without limitation on the number of chains or length, various nucleic acids can simultaneously be handled on the same base material. Thus, it can be said that the nucleic acid-immobilized substrate of the present invention can be used as a DNA array or the like with excellent performance in techniques for determining nucleotide sequences by hybridization using a number of nucleic acids such as sequencing by hybridization (SBH) and sequencing by hybridization with oligonucleotide matrix (SHOM).